Estimating occupational health events in workers with asthma or diabetes: a comparison of diary and snapshot methods

The study was set up to assess the completeness of reporting different types of work-related health events through 6 month and 1 week diaries and telephone questionnaires relating to individual days. Subjects recruited from hospital asthma or diabetic clinics or from surgical day-case units were randomly assigned to either a full participation arm or to one completing only a 6 month diary. Of the 375 study participants, return rates were 68.8% for 6 month diaries, 81.9% for weekly diaries and 86.5% for researcher-administered questionnaires. Significantly higher rates of self-reported poor work performance, symptoms or changes in medication were estimated by snapshot methods (same-day telephone interviews or one-off weekly diaries) than from diaries completed over a 6 month period. Asthmatics and diabetics attending hospital outpatient clinics were no more likely, however, to report work-related health events in the following 6 months than those attending the same hospital for day surgery.